Introduction
Many filers assume every 401(k) contribution needs a manual entry on Form 1040. It doesn't. The right treatment depends on whether you contributed, withdrew, or rolled money over.
This guide covers U.S. federal income tax reporting for traditional and Roth 401(k) activity. State rules and personal circumstances may differ, and Australian readers with U.S. accounts should note that treaty and residency rules sit on top of everything below.
The workflow is simple. Check your W-2 for payroll contributions, look for a Form 1099-R if money left the account, then decide whether anything belongs on Form 1040 or an extra form such as Form 5329.
Key Takeaways
- Traditional 401(k) contributions get their tax benefit through payroll, so you don't deduct them again on Form 1040.
- Roth 401(k) contributions use after-tax wages and don't reduce current taxable income.
- Contributions alone don't require reporting your balance or investment growth.
- Withdrawals, rollovers, excess deferrals and missed RMDs can trigger extra reporting.
How 401(k) Contributions Affect Taxable Income
Payroll exclusion, not a return deduction
Traditional employee contributions come out of your paycheque before federal income tax is calculated. Your employer excludes them from W-2 Box 1, so the figure that flows to Form 1040 line 1a is already reduced. The IRS explains this in its Topic 424 guidance.
A simple illustration: on an $80,000 salary with a $10,000 traditional deferral, Box 1 shows roughly $70,000. Social Security and Medicare wages (Boxes 3 and 5) still reflect the full amount, because pre-tax deferrals remain subject to FICA.
Entering that $10,000 again on your return would deduct it twice.
Reading Form W-2
- Box 1: federal taxable wages, net of traditional deferrals
- Boxes 3 and 5: Social Security and Medicare wages (full pay, including deferrals)
- Box 12 code D: traditional 401(k) elective deferrals
- Box 12 code AA: Roth 401(k) deferrals
Confirm the code descriptions in the current IRS W-2 instructions each year.
Traditional versus Roth
Roth deferrals are taxed now, so Boxes 1, 3 and 5 include them. Qualified Roth distributions later can be tax-free. The contribution type, not the fact it landed in a 401(k), decides whether your current taxable income is reduced.
Employer contributions
Employer matches and profit-sharing amounts generally aren't part of your current taxable wages and don't appear as your D or AA deferrals. Employer Roth contributions under SECURE 2.0 are different: they're taxable in the allocation year and reported on Form 1099-R with code G, not W-2 code AA.
Limits and excess deferrals
For 2026, the employee deferral limit is $24,500, per the IRS announcement. It covers traditional and Roth combined, across all employers. Catch-ups of $8,000 apply at age 50 and over, and $11,250 at ages 60 to 63, if the plan allows.
Excess deferrals plus earnings must be withdrawn by 15 April after the deferral year. An extension doesn't move that date. Left uncorrected, pre-tax excess can be taxed twice.
Which Tax Forms Show 401(k) Activity?
Form W-2 for payroll contributions
If you only contributed through payroll, the W-2 is your main document. Wages, withholding and Box 12 codes reconcile with your return. Plan providers don't normally issue a separate contribution statement.
Form 1099-R for money leaving the account
Form 1099-R covers cash withdrawals, rollovers and certain deemed distributions, not ordinary contributions. Key boxes:
- Box 1: gross distribution
- Box 2a: taxable amount
- Box 4: federal tax withheld
- Box 7: distribution code
Other forms
- Form 5500: annual plan return filed by the employer or plan administrator, not by you
- Form 5329: filed by you for early-distribution exceptions the payer didn't report, and for missed-RMD tax
File only what your records call for.
How 401(k) Withdrawals and Rollovers Appear on Form 1040
Start with what happened
Ask which of these applies:
- Money stayed in the plan
- You took cash
- You completed a direct rollover
- You completed an indirect rollover
- You took a partial cash-out
Receiving a 1099-R doesn't mean the whole amount is taxable.
Where the numbers go
Using 2025 Form 1040 lines (verify for your tax year):
| Activity | Entry |
|---|---|
| Fully taxable distribution | Line 5b only |
| Partly taxable distribution | Gross on 5a, taxable on 5b |
| Rollover, direct or indirect | Gross on 5a, taxable remainder on 5b, check 5c box 1 |
| Federal tax withheld (Box 4) | Line 25b |
Direct and indirect rollovers
A trustee-to-trustee transfer has no mandatory 20% withholding, yet it still appears on a 1099-R. Check that the code and taxable amount are correct. Code G isn't proof of tax-free treatment, since pre-tax money rolled to a Roth destination can be taxable.
With an indirect rollover, 20% is generally withheld and you have 60 days to redeposit. The IRS example in Publication 575 shows a $10,000 distribution with $2,000 withheld, leaving you $8,000.
If you roll over only that $8,000, the withheld $2,000 is taxable. Replace the $2,000 from other funds to roll over the full amount, and keep deposit confirmations.
Early withdrawals
Taxable distributions before age 59½ generally face ordinary tax plus a 10% additional tax, unless an exception applies. Common exceptions include:
- Separation from service in or after the year you turn 55
- Disability, death, or QDROs
- Certain medical costs
Withdrawing at 55 after an earlier separation doesn't qualify. Use Form 5329 to claim exceptions the payer didn't code.
Reporting errors
Omitting a 1099-R or misstating the taxable amount can prompt a CP2000 notice. Compare the form to your plan's year-end history and ask the administrator to fix mistakes. If a form doesn't arrive in time, the IRS allows Form 4852.
Special Situations and Common 401(k) Filing Mistakes
Roth, loans and RMDs
- Traditional distributions are ordinary income.
- Qualified Roth withdrawals need a five-tax-year period plus age 59½, death or disability.
- Non-qualified Roth withdrawals are split pro rata between contributions and earnings.
- A compliant plan loan isn't a distribution. A default can become a deemed distribution (code L) and be taxed.
- Traditional 401(k) RMDs generally start at 73. A missed RMD carries a 25% tax, reduced to 10% with timely correction.
Pre-filing checklist
- Gather your W-2 and any 1099-R.
- Collect rollover confirmations and withholding details.
- Pull plan correspondence and any corrected forms.
- Don't deduct payroll contributions twice.
- Don't report your balance or unrealised growth as income.
- Act on corrected forms that arrive after filing.
Conclusion: What to Remember About 401(k) Contributions on Form 1040
- Payroll contributions are handled through the W-2
- Distributions and rollovers bring Form 1099-R figures onto Form 1040
This article is general information, not tax advice.
VJM Global's tax team prepares U.S. Form 1040 and 1040-NR returns for clients of any nationality and advises on cross-border compliance. For help with rollovers, complex filings or treaty questions, email [email protected].
Frequently Asked Questions
Do I need to report my 401(k) on my tax return?
Ordinary payroll contributions are reflected on your W-2 and need no separate entry. Withdrawals, rollovers and other transactions generally require Form 1040 reporting.
Can I deduct my 401(k) contributions on my taxes?
Traditional contributions are already excluded from W-2 Box 1, so you don't claim them again. Roth contributions are made after tax and aren't deductible.
What tax form shows 401(k) contributions?
Form W-2, mainly Box 12 code D (traditional) or AA (Roth). You usually get no separate form for payroll deferrals.
Where do I report my 401(k) distribution on Form 1040?
Use Form 1099-R to complete the pension and annuity lines, 5a and 5b on the 2025 form. Check the instructions for your tax year.
Do I have to pay taxes on my 401(k) withdrawals?
Traditional withdrawals are taxable income. Qualified Roth withdrawals can be tax-free. Early distributions may add a 10% tax.
What is the penalty for early 401(k) withdrawal?
Generally a 10% additional tax on the taxable amount before age 59½. Exceptions exist, and Form 5329 may be needed to claim them.
